Method and apparatus for the production of pulp



Dec. 11, 1934. 'r. L. DUNBAR ET AL METHOD AND APPARATUS FOR THE PRODUCTION OF PULP Filed 001;. 5, 19 32 M MW N INVENTORS M5232 d.c}:uam

ATTORNEY Patented Dec. 11, 1934 PATENT OFF'ICE METHOD vAND APPARATUS FOR THE PRO- DUCTION OF PULP Thomas L. Dunbar, Watertown, N. I and George Fulton, Masson, Quebec, Canada, assignors to Chemipulp Process, Incorporated, Watertown, N. Y., a corporation of New York Application October 5, 1932, Serial No. 636,312

15 Claims.

invention relates to methods and apparatus for the production of pulp, and more parcooking operation. 1

The object of the invention is the provision of improvements in methods and apparatus for the production of pulp, in particular during the cooking operation. The invention results in improved distribution of heat throughout the digester contents and in an improved pulp'product.

Various proposals have been made for the circulation of digester liquor during the cooking or digestion of the pulp. The purpose of such circulation is to effect more uniform distribution of heat throughout the pulp in the digester. This circulation has heretofore been a steady fiow of liquor into the digester; Such circulation flow, however, resultsin channeling in the pulp by the .circulating liquor, with the result that the heat is not. uniformly distributed throughout the pulp mass. 1

With our improved method and apparatus, the digester liquor is circulated with an intermittent, pulsating motion. Each successive pulsation or inflow of liquor stirs up the pulp contents of the digester, which settle again between pulsations. The pulp contents of the digester are thus agitated and stirred up. Channeling by the circulating liquor is avoided and great improvement in the uniformity of heat distribution is effected.

Centrifugal pumps, which have heretofore been universally used in digester circulation, will gasbind and stop when gas is taken into the circulation line. With our apparatus, however, i3 gas should be withdrawn along with the digester liquor'no interference with the circulation results. In fact, in some-cases we prefer to withdraw gas from the upper part of the digester and circulate the same back into the lower part thereof through the liquor circulating system.

Apparatus suitable for the practice of our invention is illustrated in the accompanying drawing, in which: Y l

Fig. 1 is a diagrammatic elevation of a digester and associated circulating apparatus, certain parts being omitted for the sake of clearness; and

Fig. 2 is an elevation, partly brokenaway, showing an alternate construction. I

In the drawing, the numeral 1 indicates a pulp digester. The top relief line 2, provided with the valve 3, and the side relief line 4, provided with the valve 5, connect with the relief header 6 leading to the hot acid accumulator or other gas recovery system.

The intake end of the circulating line 11 con-v nects with the digester through the line 12 and valve 13 and also through the line 14 andvalve 5 15. The line 12 enters the top of the digester, while the line 14 enters the digester at a point below the top thereof and terminates within the digester in a strainer (not shown). The circulating line 11 discharges into the line 17. The 10 line 17 discharges through the check valve 16 into the plunger pressure pump 20.

The pump 20 is provided with a plunger '21, which in Fig. 1 is shown as operated by means of a steam cylinder 25. The pump 20 discharges 1 through the line 23 and check valve 24 into the exchange heater 30. The exchange heater connects through the line 31 and valve 32 with the lower part of the digester, preferably through the blow-off elbow 8. 20

The line 26, provided with the valve 2'7, connects the exhaust ports of the steam cylinder 25 with the exchange heater 30, and permits the utilization of steam from thesteam cylinder as a heating medium in the exchange heater. The 25 line 28 is provided to carry off condensate from the heater, and may lead to the hot well or otherpoint of utilization of the condensate.

The steam line 36, provided',with the, valve 37, leads from any suitable steam supply into the 30 bottom of the digester, and by this means steam may be directly introduced into the digester when desired.

The pump 20 may be a single-acting pump as shown in Fig. 1, or it may be a double-acting pump as illustrated in Fig. 2. In the case of the double-acting pump, the line 41 provided with the check valve 42, leading from the circulating line 11, and the line 43 provided with the check valve 44, connecting with the line 23, and both .40 connecting with the pump 20, are provided as shown in Fig. 2. I

Instead of the steam cylinder illustrated in Fig. 1,-the pump 20 may be operated by a lever as indicated generally at 50 in Fig. 2, or any 45 other suitable motive powermay be provided. I

In' case it is not desired to employ the exchange heater 30 the connection from the circulating pump may be direct to the digester through the line 23 and valve 48, as shown in Fig. 2.

Operation in accordance with our invention may be as follows:

The digester is charged with chips in the usual manner and is then filled with liquor through. the liquor filling line (not shown). Our invention is applicable to either hot or cold acid digestion processes. When used in conjunction with hot acid systems, the liquor need only be circulated until the temperature in the digestef reaches about 110 C. When starting with cold acid, however, the circulation should be continued until the exhaust stroke of the plunger, the valve 16 closes and the valve 24 opens, the liquor passing through the line 23 into the heater 30 or direct to the lower part of the digester.

The digester liquor is heated either by the direct admission of steam into the digester through the line 36 or by means of the exchange heater 30. If a steam cylinder is employed to operate the pump 20, steam from the exhaust ports of the cylinder may be passed through the line 26 and valve 27 to the exchange heater for the purpose of heating the liquor therein, or any other suitable heating medium may be employed.

After the side reliefliquor has been drawn ofi from the digester, circulation is continued through the line 14' and valve 15.

Gases from the digester may be drawn into the circulating line 11 and passed through the pump '20 and back into the digester without interfering with the circulation. Gas will be circulated in this manner, for example, when the circulation intake is through the line 12.

During the latter part of the cook digester gases are relieved through the line 2, valve 3 and header 6 to the hot acid accumulator or other'recovery system.

The reciprocation of the plunger 21 passes the circulating liquor into the bottom of the digester intermittently, giving a pulsating circulation. Each pulsation lifts 'and stirs the pulp inthe digester. Channeling is prevented and uniform distribution ofheat through the digester contents is efiected.

When using a double-acting pump, as shown in Fig. 2, the lines 41 and 43 and check valves 42 and 44 operate similarly to the lines 17 and 23 and I but the momentary check at the end of each' plunger stroke produces noticeable pulsations.

While the rate of circulation and the frequency of the pulsations may be varied, it may be said by way of example that using a pump with a capacity of approximately 1/250 of the digester capacity, we have obtained excellent results operating the pump at the rate of 10 to 16 strokes per minute, or with a circulation ratio of 1/15 to 1/25 of the digester contents per minute. 'I'hese figures are not given in a limiting sense, however, but merely by way of an example of the practice of our invention.

We claim:

1. In the digestion of fibrous material, withdrawing liquor and gas from the upper part of a digester and returning said liquor and gas together to the lower part of the digester in a pulsating stream.

2. In the digestion of fibrous material by the V sulfite process, charging a digester with fibrous material and with acid liquor, digesting said material in said liquor under heat and pressure, and during the said digestion withdrawing liquor from the digester and agitating the fibrous material by returning withdrawn liquor under successive pressure impulses to the bottom part of the digester. L

3. In the digestion of fibrous material by the sulfiteprocess, charging a digester with fibrous material and with acid liquor, digesting said 'fibrous material in said liquor under heat and pressure and circulating said liquor during such 4. In a process of the character described,

charging a digester with fibrous material and with digestion liquor, digesting said material in said liquor under heat and pressure, and during the said digestion withdrawing liquor from the digester and agitating the fibrous material by returning withdrawn liquor under successive pressure impulses to the bottom part of the digester.

' 5. A process as described in claim 4 in which the successive pressure impulses of the liquor introduced into the bottom part of the digester follow each other at time intervals of less than one minute.

6. In the digestion of fibrous material, withdrawing digestion liquor from a mass of fibrous material during the cooking thereof and returning said liquor to thelower part of the mass of fibrous material during the cooking thereof in a pulsating stream.

7. Treatment of digestion liquor in accordance with claim 6, in which the liquor is indirectly heated after its withdrawal from the fibrous mass and before its return thereto.

8. In the digestion of fibrous material, circulating the digestion liquor during the cooking of the fibrous material by withdrawing said liquor from the upper part of a digester and returning the same to the lower part of the digester in an intermittent pulsating stream.

9. In the digestion of fibrous material, withdrawing digestion liquor from a mass of fibrous material and returning said liquor to the fibrous mass during the cook in a pulsating stream at a rate of one-twentieth to one-twenty-fii'th of the capacity of the digester per minute.

10. In the digestion of fibrous material, withdrawing gas from the upper part of a digester and returning said gas to the lower part of the digester in a pulsating stream during the cooking of the fibrous material, whereby the cooking liquor is strengthened in the digester.

11. In apparatus of the character described, a digester, a conduit from the upper part of the digester connecting through a pluralityof entrances thereto with the suction sideot a plunger pressure pump, a conduit connecting the outlet side of said pump through a plurality of exits therefrom with the lower part of the digester, and means for operating said pump, whereby liquor may be withdrawn from the digester and returned thereto in two pulsations to each complete reciprocation of the plunger.

12. In apparatus of the character described, a digester, a circulation conduit connecting with the interior of the digester through a plurality of entrances at difierent levels into the upper part of 13. In apparatus of the character described, a digester, a conduit connecting the upper part of the digester with the lower part thereof, a plunger pressure pump interposed in said conduit and means comprising a steam cylinder for operating said. pump, an indirect heat exchanger interposed in the conduit and a conduit from the steam cylinder to the heat exchanger, whereby exhaust steam from the cylinder may be conducted to 10 the heat exchanger.

14. In the digestion of fibrous material by the sulfite process, circulating the digestion liquorduring the cooking of the fibrous material by withdrawing said liquor from the upper part of the digester and returning the same to the lower part of the digester in a pulsating stream.

15. In the digestion of fibrous material by the sulfite process, withdrawing cooking liquor from the upper part of a digester and agitating the fibrous material in the digester by returning the withdrawn liquor to the lower part of the digester in a. pulsating stream.

THOMAS L. DUN'BAR. GEORGE E. FULTON. 

